Drainage Flow Options

  • Slope algorithm to use for downhill drainage vectors. This can be different than that used for other operations.  You should be very careful changing this.
  • Show
    • Point slopes:  slope is computed at a point.  The vector length isproportional to the slope at the point.
    • Region vector average: slope is computed at all points in a box, and the vector average is plotted.  The vector magnitude is proportional to the resultant vector magnitude (1 if all vectors point in the same direction, 0 if they are completely randomly distributed).
  • Distance in map pixels that DEM grid postings will be separated when a vector will be drawn.  This effectively reduces the number of vectors drawn.  Zooming in will have vectors drawn closer together in gound distance.
  • For each computation method
    • Vector color and line width
    • Length of vectors (scaling factor)
    • Region size
      • For point slopes, this is the distance to go out to pick the 8 points to use in the slope algorithm
      • For region vector averages, this is the size of the region to use with computation of every point.
  • Force screen redraw

Overlay with the two options.

  • They generally agree in direction, but where the aspect varies, they can give different results.
  • Since it can be challenging to show every point's aspect vector, some smoothing may give the best results. 

Sample graphic and directions for getting it.

Last revision 5/20/2019